1. Field of the Invention
The present invention relates to a control device and a method for controlling a variable valve timing mechanism which varies valve timing of an engine valve (an intake valve or an exhaust value) of an internal combustion engine.
2. Description of Related Art
A control device of this type of variable valve timing mechanism controls valve timing by detecting the rotation phase of a camshaft with respect to a crankshaft and bringing the rotation phase close to a target rotation phase by using the variable valve timing mechanism.
In a control device of a variable valve timing mechanism disclosed in Japanese Patent No. 4123127, in a variable valve timing mechanism which drives a camshaft for opening and closing an intake valve using an electric motor, rotation signal of a motor shaft, of which frequency of detection per unit rotation angle of a camshaft is large compared with a rotation angle sensor provided on the camshaft, is used, thereby achieving the valve timing control with high accuracy in an engine lower speed area.
However, the crankshaft may rotate in a reverse direction to a forward rotation direction (reverse rotation) at a time of extremely low rotation of an engine just before a stopping, such as when operation of the engine is stopped. In the control device of the variable valve timing mechanism disclosed in Japanese Patent No. 4123127 described above, in a case of reverse rotation, the rotation phase of the camshaft cannot be detected correctly. Thus, for example, in a case in which a valve timing of the intake valve is controlled to a valve timing for starting during engine stopping process, preferable valve timing control has not been achieved.